This paper presents the effect of different bias circuits configurations on the noise performance of GaAs HBT (heterojunction bipolar transistor) power amplifiers at the receiver band. Various bias circuits have been used for the power amplifier in an WCDMA (wideband code division multiple access) transmitter module including the output duplexer at PCS band (Tx: 1850 ∼ 1910MHz, Rx: 1930 ∼ 1990MHz). A bias circuit with cascode current mirrors for the 1^st and the 2^nd stages shows less than -180dBm/Hz receiver band noise with -39dBc of ACPR (adjacent channel power ratio) at 25.2dBm antenna output power.